The present invention relates to brick for use in the construction of furnace linings for metallurgical applications.
At the present time, magnesite-chrome and chrome-magnesite brick are widely used for this purpose and are made in a number of ways. Thus, deadburned magnesite can be simply mixed with chrome ore and pressed into brick shapes that are then fired to effect ceramic bonding. These are generally fired at a high enough temperature to obtain a substantial amount of bonding between the deadburned magnesite and the chrome ore and thus such brick have been termed "direct bonded brick" to distinguish them from brick burned at lower temperatures.
In brick burned at lower temperatures, the accessory silicate minerals from the deadburned magnesite and chrome ore form the primary bond and thus this type of brick is often referred to as "silicate bonded brick" and do not generally have sufficient enough corrosion resistance to be used in applications where there will be particularly severe environments. It is also known, however, that while direct bonded brick outperform the silicate bonded brick in the severe service environments, even the direct bonded brick are subject to slag attack because of their relatively high porosity. Efforts to lower the porosity of these bricks has proven to be difficult because the brick expand in burning. One effort to eliminate the porosity problem is to make the brickmaking grain from a fine magesite and chrome ore. This type of grain is often called "coburned" grain. It can be made, for example, by briquetting fine magnesite and fine chrome ore and firing the briquettes to effect densification and ceramic bonding. Alternatively, a mixture of fine magnesite and fine chrome is fed to a rotary kiln where the rotating action of the kiln produces the desired agglomerates. Other methods of producing coburned grain are also known and utilized. This coburned grain is then crushed, graded, and ball milled into appropriate brick making fractions and used to make brick in a conventional manner. On firing, such brick typically shrink rather than expand and the final brick have a lower porosity than direct bonded magnesite-chrome brick.
Another manner of making a low porosity brick is to make fused magnesite chrome or fused chrome magnesite grain. The fused grain is made by charging deadburned magnesite and chrome ore into an electric arc furnace where the mixture is melted. The melt is then allowed to cool to room temperature and the solidified material is crushed and graded resulting in extremely dense, low porosity grain. The fused grain is used to make the densest, lowest porosity magnesite chrome and chrome magnesite brick available. These brick are often referred to as "rebonded fused magnesite-chrome brick" or "rebonded fused chrome-magnesite brick", depending on the relative proportions of the minerals. These rebonded brick are characterized by excellent resistance to chemical attack as from slag. However, they have poor thermal shock resistance.